Measuring instrument



April 5, 1938. G. A [SING MEASURING INSTRUMENT Filed July 28, 1955INVENTOR m wm 5% T w m O D. A F m 5V B G Patented Apr. 5, 1938 v UNITEDSTATES PATENT OFFICE MEASURING INSTRUDIENT Gustaf Adolf Isins, Stocksundat Stockholm, Sweden Application July 28, 1933, Serial No. 682,649 InSweden August 25, 1932 Claims. (Cl. 73-151) The present inventionrelates to measuring inbahm b a h b t ted through a, slight strumentscomprising a measuring member that is angle, and Figure 7 shows anotherembodiment easily movable about a stable position of I of the astatizedpendulum. equilibrium and adapted to deviate from said The general ideaof astatization will be readily 5 stable position of equilibrium underthe influence understood if an astatized system is first con- 5 ofexternal forces dependent on the quantity to sidered separately,assuming for the sake of be measured. Examples of such instruments aresimplicity that the easily movable part of said galvanometers,electrometers and balances in system is rotatable about a fixed axis.When no which the quantity to be measured is a-current, external forcesare present said movable part 10 or a charge or potential difierence, ora mechanitakes up a certain stable zero position. When 10 cal mass. themovable part makes a deviation :2, and in the It is often desirable tobe able to measure exassumed case rotates the extent of an angle a:tremely small deviations of the measuring memfrom its zero position, acouple ber which cannot be observed by means of ordinary optical readingdevices, as for example 4 m h through mirror reading or throughmicroscopic acting the movable part is set w c reading couple isproportional to the deviation. The The present invention has for itsobject to negative sign indicates that this couple tends to tend greatlythe possibilities oi observing exceedrestore g z ag ga g g f 22:3 :3

sys em zeropos 1 n. may Small deviations and consists essentially m Dois generally termed the directive force of the 20 mechanically combiningthe measuring instrumovable system or, more particularly, thestabilizment proper or the primary system wlth an ing directive force.As a directive force, for

astatized se'-onda or indicator tern the deflection of w hich rifle tothe astatiza zion becomes example' the torsional elasticity of asuspension filament, will serve, and thus it is now possible a multi leof that of the rima stem and 26 thereby will be more readily ob s erf'able. The by ,applying an electrostatic field to cause the indicatorsystem comprises an easily movable easny movable part of the astatizedsystim to be member adapted to serve as an indicator which is influencedby an additiofml couple Q which astatized, i. e. is influenced by twoopposing untemcts the is Pmpm" 30 directing forces which are mutually sobalanced tional to h deviatlon Tms couple can be that the deviation ofthe indicator caused through expressed by the equatmn the deviation ofthe measuring member in conse- Y Q"=k:r quence of the mechanical,cmlpling 15 multiple where k 0. The constant k represents a labilizofthe first mentwned deviatlon' ing directive force and the correspondingcouple mYentlon will b more described Q" tends to movethe easily movablepart of the 3 with, refetpence to the accompanymg drawing system awayfrom zero position. The couple reshowmg diagrammatically differentembodiments sumng from both directive forces is of the invention. Insaid drawing Figure 1, for H the purpose of explaining the meaning ofthe Q=Q (D k)$= Dx 40 terms astatize or astatization, illustrates anTheresulting directive force D must be positive 40 astatized system inwhich the labilizing directing in order to make the system stable, thusforce opposing the stabilizing directing force is b produced by anelectrostatic field. Figure 2 shows an embodiment of the invention inwhich a It is convenient to define a quantity the movable measuringmember or indicato of I k h 5 an electric, measuring instrumentismechanically D D Ics l 1 coupled with the'astatized system according toas a measure for the degree of astatizism-, which F u igu e 3. Shows anth r manner of maybe called the astatization numben: P Y bringing.aboutthe coupling, with the indicating I -th astatized system of Figure1, the easily System 18 3919., m ur i nt. movable part'consists of ametallic frame l sup- 50 Figure i,shows-anaslsatizedsystem in;which theported on a suspension filament 'l 'between twolabilizing-directingiorce is produced by the gravistationary'metalplates '3 and occupy its tational field; and Figure ,5, showsanapplication zero position (a:=0) an intermediate P05111011 of saidastatized system:in:a'.balance.--' Figure-6 "between'said two plates. Itwillbe assumed that is a ,view .or the Fig. 5-embodiment wherein the fthe suspensioii fllamentf l 'is'secured 'at its uppe ss end in a fixedsupport. The two plates 3 can be charged from a battery to opposite butnumerically equal potentials .*-V, whereas the frame 2 is held at zeropotential. When there is no electrostatic auxiliary field (V=0) theframe will be influenced only by the couple ---D :z: but as soon as V isgiven a value different from zero an additional positive couple isproduced which for small deviations will be equal to lam, where k asbefore represents the labilizing directive force. The value of k isIc=c.V where c is a constant dependent on the geometric configuration ofthe electrostatic field. If, on the other hand, the frame 2 is chargedand the plates 3 are held at zero potential a similar result is obtainedexcept that the constant 0 receives another value. The resulting couplebecomes -(Dok)x=-D:r.

The astatized' system illustrated in Figure 4 agrees in principle withthat of Figure 1. In both cases astatization is brought about by meansof a static field of force, but the only difference is that in Figure 4the gravitational field is used instead of the electrostatic field ofFigure 1. The movable part in Figure 4 consists of a standing pendulum Iwhich with its lower thickened end is fixed to a wire 8 horizontallystretched in a holder 9. The pendulum is thus adapted to oscillate aboutthe horizontal axis of the wire and stands vertically when occupying itszero position. The torsional elasticity of the fixing wire 8 producesthe stabilizing directive force Do.

, directive force is k=mgi3 where m is the mass of astatizing of thependulum then will be highly the pendulum rod, r the distance of itscentre of gravity from the axis of rotation and g the acceleration ofgravity. A deviation of the pendulum I about the axis of the wire 8 thusproduces a couple acting on the pendulum according to An astatizedpendulum may also be provided with an inclined axis of rotation althoughthe dependent upon occasional fluctuations in the inclination of theaxis, 1. e. rotations in'the plane of the drawing. For this reason ahorizontal axis of rotation is preferable.

Thus the term astatization as used in this specification represents ageneral idea which applies to all embodiments of the present inven-'tion. Figures 1 and 2 illustrate only simple examples. Movable systemscomprising magnets or conductors carrying current may also be astatizedby magnetic fields. Astatized systems are known per se, and in suchknown systems, the two directing forces Do and k' refer to one and thesame stationary system of coordinates, the movable part, for examplebeing suspended as' in Figures 1 and 4 or secured to a stationarysupport. The present invention involves a particular application of suchknown astatized systems forrobtaining as great a multiplication aspossible of the deviation'in a sensitive measuring instrument,

In the embodiment of the invention shown in Figure 2, the astatizedsystem of Figure 1 is cou- The conditions prevailing in such a combina-,

tion of a primary measuring member and an The labilizing i astatizedsystem mechanically coupled therewith are readily explained by a simplemathematical reasoning, and it will be assumed that the deviations areso small that the couples produced are proportional to the deviations.When no external force acts on the coil 4 the coil occupies its zeroposition and the frame 2, which is adapted to turn coaxially with saidcoil also occupies its position of rest, intermediately between the twocharged places 3. It will now be assumed that the coil 4 makes adeviation an and that it is held in this position. The frame 2 thenmakes a deviation x: which on account of the astaticism is several timesgreater than $1. The frame 2 is acted upon by the two couples Q:Do(a:z-a:1) and Q=kxz. The position of equilibrium of the frame 2 isdetermined by the condition Q'+Q"=0, wherefore -Do(a:::c1) +kn=0 andconsequently (Equation A) B6 &.=

As already pointed out, this value of $2 is correct, provided that coil4 has stopped in position as. The value of 0:: defined by the equationis evidently approximately true also during the movement of the coil4.11 said movement is slow' in relation to the setting movement of theframe 2. The quantity N is the astatization number of the secondarysystem, calculated under'the assumption that x; is constant andindependent of :m. The greater the number N, the greater :0: will becomein relation to :m.

Whereas in Figure 2 the electrostatic field remains at rest and thesupport of the secondary system (which is represented in Figure 2 by theupper end of the suspension filament I, secured to the coil 4) followsthe deviation of the primary system, the conditions illustrated inFigure 3 are different to the extent that the support of the secondarysystem 2 is arranged stationary as in Figure 1, whereas the astatizingfield is movable. In Flgure 3 one of the two charged plates 3 isconnected by a rigid connection 8' with the coil and thus turns togetherwith the coil, whereby the electrostatic field is subjected to adisplacement. In this case Q=-Duxz and Q' '=k:m+ax1, where a denotes acoefilcient whereof the absolute value is generally of the same order ofmagnitude as k. The coefiicient a may preferably be expressed a=b.lc,where b is a numerical factor. The deviation $2 in the condition ofequilibrium, assuming a fixed value of it: can then be calculated fromthe equation (Equation B) .It should be noted that when the astatizincoefllcient N 0 the secondary system reacts on the primary system, sothat in the condition of equilibrium the deviation x1 for a certainexternal couple becomes greater than if there were no coupling with thesecondary system. In other words, the stabilizing directing force Aacting on the primary system becomes smaller than that value A0 assumedby the directing force when N=0. Calculation shows that in the case ofFigure 2, the equilibrium of the coupled system (immobile or fixedfield) is stable only under the condition NDKM, and that in the case ofFigure 3 (movable field) it is stable only under the condition A, ND

These conditions determine an upper limit for the product NDo for givenvalues or A0. When determining suitable values for N and Doconsideration should be given also to moments of inertia, desired timeof oscillation, etc.

With reference to Figure 3 is should also be pointed out that inrotating coil 4, not only is the position of the field varied but alsothe strength of'the field acting on the frame 2, whereby also thecoefiicient k is subjected to a change proportional to. the magnitude of3:1.

Since it has beenpresupposed, however, that the deviations are so smallthat powers of 2:1 and 2:: higher than the first may be neglected, theEquation B still holds true.

The use of gravity for bringing about astatization is suitable when theastatizing coefilcient N should be great. Due to the invariablecharacter of the field of gravity, a very constant value for thelabilizing directing force It is obtained. For a measuring member havinga horizontal axis of rotation, an astatized system comprising avertically disposed or standing vertical pendulum is used.

Figs. 4 to 6 show an example of such an application. In the embodimentaccording to Figs. 4 to 6, I 8 represents the beam of the balance whichis suspended in elastically flexible bands or filaments l2, l2 fastenedto the ends of a traverse bar I! rigidly connected with the beam I0,said bands replacing the ordinary knife edges in order to entirely avoidany frictional effects, and II are the pans of the balance. The tongueof the balance consists of a rod-shaped member I, the lower enlarged endof which is secured to an elastic filament 8 which is suspended undertension between the ends of a bow-shaped holder 8 (compare Fig. 4 of thedrawing) rigidly secured to the beam l8.- The mutual arrangement of thevarious members is such that the rodshaped member I is disposedperpendicularly to the filament 8, while the latter extends in adirection parallel with the horizontal axis of rotation of the beam l8.

, In Fig. 5, the beam Ill occupies its horizontal position. In thisposition of the beam the rodshaped member or tongue 1 is verticallydisposed. A vertical line through the center of gravity b of the tonguepasses through the filament 8 supporting the tongue, so that in thevertical position of the tongue no turning moment is exerted by theforce of gravity on the tongue member in respect to its elasticsupporting axis 8. Such a turning moment is, however, set up as soon asthe tongue is deflected by some external force either to the left or tothe right. As long as the beam l8 remains horizontal, the turning moment01' reaction set up in the suspended filament 8 as a result of thetwisting thereof is, nevertheless, greater for every angular position ofthe tongue than the turning moment of gravity, and hence, as soon as thetongue is released, it will immediately return to its vertical position.When the beam l8 occupies its balanced horizontal position, the verticalposition of the tongue thus resolves into a stable position ofequilibrium.

In Fig. 6, beam III has been rotated to an angle 1:; from its horizontalposition, and this rotation causes the pivoted points of the filamentmovement.

8 to turn a corresponding angle in relation to the horizontal, and thusalso in relation to the direction of the gravity field of force. Theturning of the pivotal points of the filament 8 will obviously cause adeflection of the tongue member 1 from its vertical position, so thatthe force of gravity is caused to exert a turning moment on the tongue,assisting in deflecting the same. The deflection of the tongue 1 stopswhen it has rotated through an angle in relation to its support 8 havinga value 1122 which is such that the restoring moment set up in thefilament as a result of the twisting thereof, is equal to the turningmoment imposed on the tongue by the gravity field of force. The totaldeflection w1+$z of the tongue 1 is thus always greater than thedefiection an of the beam l8.

As will be clear from the above, the effect of the field of force (inthe case considered, the gravity field of force) upon the secondarymemher (in this case the tongue 1) increases with the deflection of themeasuring member, (the beam l0) and for this reason a small deflectionof the measuring member can result in a great total deflection of thesecondary member.

In the embodiment of the invention illustrated in Fig. 2 of the drawing,the electric field of force produced between two charged metal plates 3is utilized to influence the secondary member 2, and when this memberoccupies exactly a middle position between the two plates 3, the totalcharge of electricity on it will be zero, and there is no resultingattraction or repulsion between the secondary member and the plates' Ifthe filament l, on account of a deflection of the measuring member 4,which by means of the clastically yielding suspension, is mechanicallycoupled with the secondary member 2, the latter is moved away from itsmiddle position, and the symmetry of the arrangement will be disturbed,while the secondary member will receive a charge of such sign that theattraction from one of the plates 3 assisted by the repulsion from theother plate 3 will tend to move the secondary member a distance furtherin the direction of its initial This force exerted on the secondarymember will, for small displacements, be proportional to thedisplacement of the member from its position to equilibrium. Thedisplacement of the secondary member will stop when it has beendeflected such an angle in relation to the measuring member that thetorque of reaction set up in the twisted filament l counterbalances theturning moment caused by the force from the electrostatic field offorce.

Fig. 7 shows another embodiment of the astatized pendulum supported onthe beam l0, which latter is shown as in Fig. 4 in transversal section.The pendulum 1 in Fig. 7 consists in a vertical rod tapered at its lowerend to a fiexible elastic stem 8', which in this case forms the yieldingconnection between the beam and the pendulum and corresponds to theelastic filament 8 in Fig. 4.

The axis of rotation of an astatized pendulum need not necessarily behorizontal. If the axis of rotation is inclined in relation to thehorizontal plane and forms an angle with the latter the labilizingdirective force becomes k=mar.cos Generally it'is preferable to have theangle 5:0, as a greater constancy of k is then obtainable, since thederivative for {:0, is equal to zero, wherefore accidental changes ofinclination have then no appreciable influence.

Such systems have been primarily considered in the preceding descriptionwherein the deviations x1, x: consist oi rotations about definite.

, and directing force" in a more general sense.

If, for example, the variation of the position parameter a: is a truerendition, the couple Q obtains the meaning of a force in the propersense of the word, and the directing force" Do then means that whichcould be termed a spring constant, i. e. that coefficient of which theproduct with the displacement :1: gives the restoring force.

I wish it to be understood that I do not desire to be limited to theexact details of construction shown and described. since obviousmodifications will occur to those skilled in this art.

I claim:'

1. In a measuring instrument, the combination, with a balancingmeasuring member, frictionless,

elastic suspending means exclusively supportingsaid measuring memberintermediate the ends thereof and allowing frictionless motion thereof,an upwardly directed indicator member, an elastically yieldingconnection fixed upon the intermediate portion of said measuring memberabove the point about which said measuring member moves so as to swingabove said point with the measuring member, said elastically yieldingconnection exclusively supporting said indicator member and allowing thesame also to move in unobstructed manner relatively to said measuringmember with freedom from friction and from contact with the rest of. theinstrument, and

there being a static field of force operating upon said indicator membertending to accentuate any occurring deflection of the indicator member;-

from upright position by neutralizing the greater part of the elasticcoefficient of restoring force inherent in the elastically yieldingconnection which tends to restore the indicator member to uprightposition upon return of the measuring member to even balance.

2. A measuring instrument according to claim 1, wherein a pair ofupwardly extending spaced supports are fixed upon the intermediateportion of the measuring member and the elastically yielding connectionis attached to said spaced supports.

3. A measuring instrument comprising the combination, with a balancebeam, of elastic sus- Pension means for said balance beam intermediatethe ends of said beam allowing frictional movement-thereof about asubstantially horizontal axis, an indicator member carried upon saidintermediate portion of the beam and comprising a standing pendulum, andan elastically yielding support forming an exclusive and frictionlessconnection between said intermediate portion of said beam and saidpendulum allowing frictionless movement of the pendulum relatively tothe beam with freedom from contact with all other portions of theinstrument, the weight of said pendulum being sufiicient to cause theelastic eoefilcient of restoring force of the elastically yieldingsupport which tends to restore the pendulum to upright position innormal position of the balance beam to be neutralized by gravity so asto accentuate any occurring deflection of the pendulum from uprightposition due to movements of the balance beam.

4- In a measuring instrument having a balance beam mounted intermediatethe ends thereof for movement about a horizontal axis and a standingpendulum forming an indicator member carried upon said beam, thecombination of elastic suspension means for said beam supporting thesame at the intermediate portion thereof and forming the sole connectionbetween said beam and the other portions of the apparatus supporting thebeam so as to allow frictional movement of the balance beam about saidhorizontal axis, and an elastically yielding support fixed upon saidintermediate portion of said beam and directly carrying said pendulumabove said horizontal axis and allowing frictionless movement of thependulum relatively to the beam in complete freedom from contact withany other portion of the instrument, and there being a static field offorce operating upon said pendulum tending to accentuate any occurringdeflection of said pendulum from upright position by partly neutralizingthe greater part of the elastic coefiicient of restoring force inherentin the elastically yielding support which normally tends to restore thependulum to upright position upon return of the balance beam to evenbalance.

5. In a measuring instrument, the combination, with a suspendedswingable measuring member of a frictionless, elastic suspending meansexclusively supporting said measuring member and allowing frictionlessmotion thereof, an indicator member, an elastically yielding connectionfixed to said measuring member so as to swing with the same measuringmember, said elastically yielding connection exclusively supporting saidindicator member and also allowing the same to move frictionlessiy inunobstructed manner relatively to said measuring member from a normalposition and with freedom from contact with the rest of the instrument,and there being a static field of force operating upon said indicatormember tending to accentuate any occurring deflection of the sameindicator member from normal position by neutralizing the greater partof the elastic coefllcient of restoring force inherent in saidelastically yielding connection which tends to. restore the indicatormember to normal position upon return of the measuring member to itsnormal position.

- GUSTAF ADOLF ISING.

